1. Field
The invention is related generally to the field of factory automation, and more particularly, to the application of factory automation for an airplane assembly and build process.
2. Background
Work cell and factory level automation for an airplane assembly and build process usually is comprised of specific work cells for forward and aft fuselages, respectively. A typical work cell includes multiple cradle fixtures to hold and position the fuselage assembly and a workstand. Work cell and factory level automation typically requires that Automated Guided Vehicles (AGVs), which carry robots on both the inside and outside of the fuselage, achieve demanding positional accuracy and repeatability relative to the fuselage assembly on a cradle fixture, in order for the robots on the AGVs inside the fuselage to work in a coordinated manner with the robots on the AGVs outside the fuselage.
Path planning and navigation for the AGVs outside the fuselage are guided by laser scanner sensors mounted on each of the four sides of the AGV. These laser scanner sensors are able to measure the distance to an object in its Field of View (FoV) and these ranging distances to objects within its Field of Regard (FoR) are used by an AGV controller to construct a contour or map in a two-dimensional (2-D) plane of view for use in the path planning and navigation.
There are two areas for improvement: (1) the AGV's accuracy and repeatability in returning to taught node positions within a particular work cell, and (2) the AGV's ability to use the same taught node positions, with cradle fixtures and a workstand within the particular work cell, across other work cells using other sets or copies of similar cradle fixtures and workstands.
With regard to area (1), the AGV, as it approaches or is at the taught node position within a work cell, adjacent to cradle fixtures and/or a workstand, may use any or all of the laser scanner sensors on each of the four sides of the AGV. However, from an operational perspective, the laser scanner sensor that is directly facing and/or adjacent to the cradle fixtures and/or workstand is the ideal one to be used. The other laser scanner sensors that are on the back and sides of the AGV may or may not be able to effectively view the target features on the cradle fixtures and/or workstand. The laser scanner sensor being used by the AGV scans across 190 degrees in discrete steps, whereby it measures the distance to the object within its laser beam path using an optical pulse time-of-flight measurement principle. Distance measurements to the object within the laser scanner sensor's beam path include systematic or bias and statistical random errors. The laser scanner sensor's 5 sigma measurement error (systematic or bias and statistical random errors) is an order of magnitude greater that the desired AGV accuracy and repeatability in returning to the taught node positions within a work cell and hence simple measurement averaging of the measured distances will not be adequate.
With regard to area (2), the AGV's ability to use the same taught node positions, with the cradle fixtures and workstand within the particular work cell, across other work cells using other sets or copies of similar cradle fixtures and workstands, is a challenge due to variability in the objects other than the target features within the laser scanner sensor's Field of Regard (FoR) and Field of View (FoV) within the particular work cell. It is assumed that the target features on a cradle fixture or workstand in a work cell are replicated, with metrological accuracy, on other sets or copies of similar cradle fixtures and workstands across other work cells. Given that the laser scanner sensor scans across 190 degrees and with a ranging distance specification of 49 meters, there is a high likelihood that, in an operational environment, other static and dynamic objects other than the target features on the cradle fixture and workstand may be picked up, and thereby cause mapping ambiguity and issues with the AGV's path planning and navigation to move to the desired node position within the work cell adjacent to the cradle fixtures and/or workstand.
Therefore, there is a need in the art for improvements to the application of factory automation for an airplane assembly and build process.